1. Field of the Invention
This invention relates to refiners which prepare fibers for use in paper-based products including papermaking, and to disc refiners in particular.
2. Description of Related Art
For papermaking purposes, wood chips or another raw fiber source are ground into smaller chips or mechanically treated so that the chips may be broken down further and refined into individual fibers. After refining, these individual fibers are typically used to make paper related products, such as sheet paper, toilet paper, paper towels, and other absorbent products.
Disc refiners are used to break down clumps of fibers into individual fibers. A disc refiner typically utilizes pairs of opposed refiner discs. A refiner disc is a disc-shaped steel or steel-alloy casting which has an array of generally radially extending bars or upraised ridges formed in its refining face or refining surface. The refiner disc may be formed of one or more continuous annular discs, or may instead be formed of a plurality of refiner disc segments arranged to form a ring or annulus.
One refiner disc is mounted on a rotor for rotation and the other disc is mounted on another mounting surface opposed to the first refiner disc such that both discs face each other and are very close to each other. The other mounting surface may, for example, be a mounting surface that does not move during refiner operation or another rotor which turns in a direction opposite the first rotor. As wood pulp passes between the opposed refiner discs, relative rotation between the opposed discs desirably refines the pulp.
The flow of vast volumes of stock between the refiner discs inevitably results in wear of the discs, eventually necessitating their replacement. In order to minimize down time and maximize production of the refiner, it is desirable that disc replacement be done as quickly as possible.
However, during the refining operation, extractives and baked fiber are produced and act essentially as a glue that holds the refiner disc against its mounting surface. Therefore, removal of the refiner disc is generally very difficult, time consuming, and ordinarily cannot be achieved by simply removing the mounting bolts that attach the refiner disc to its mounting surface.
U.S. Pat. No. 5,526,992 to Hawen et al. discloses a refiner disc having a plurality of mounting bores and at least one removal hole. The mounting bores extend through the refiner disc and permit the disc to be attached to a mounting surface using bolts. The removal hole extends completely through the refiner disc.
During use of the refining disc, the threaded removal hole is filled with a relatively short covering screw that has a head at its free end which is received in a counterbore of the removal hole. The headed covering screw prevents fibers from penetrating between the disc and the mounting surface. In order to remove the disc, the covering screw is removed and replaced with a second, longer removal screw referred to as a "bursting" screw that is disclosed as having a length longer than the thickness of the disc. The removal screw is threaded into the removal hole completely through the disc until its end bears against the disc mounting surface. Further rotation of the removal screw applies a pressure against the mounting surface that causes the disc to be urged away from the mounting surface enabling it to be removed.
A primary disadvantage of this approach is that it requires two different screws and thus is not of integral construction. This creates the possibility that one of the screws may become lost while the other screw is in use. Therefore, an improved method and device which does not require the use of two separate screws would be very advantageous.